KR101111705B1 - ND filter and aperture diaphragm apparatus - Google Patents

ND filter and aperture diaphragm apparatus Download PDF

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KR101111705B1
KR101111705B1 KR1020050040254A KR20050040254A KR101111705B1 KR 101111705 B1 KR101111705 B1 KR 101111705B1 KR 1020050040254 A KR1020050040254 A KR 1020050040254A KR 20050040254 A KR20050040254 A KR 20050040254A KR 101111705 B1 KR101111705 B1 KR 101111705B1
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South Korea
Prior art keywords
film
light absorbing
nd filter
optical
light
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KR1020050040254A
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Korean (ko)
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KR20060047909A (en
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고키 구니이
가즈토시 무카에
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니덱 코팔 가부시키가이샤
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Priority to JP2004145541A priority patent/JP4481720B2/en
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    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/20Filters
    • G02B5/22Absorbing filters
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/20Filters
    • G02B5/205Neutral density filters

Abstract

The ND filter is made of a transparent substrate having a plane. The optical film is formed on the plane of the transparent substrate. The optical film has a laminated structure including a light absorbing film and a dielectric film, and has a varying transmission concentration. The thickness of the light absorbing film or the dielectric film of the laminated structure is changed in the in-plane direction of the transparent substrate so as to control the transmission concentration of the optical film stack to change in the in-plane direction. The light absorbing film is made of a material selected from Ti, Cr, Ni, NiCr, NiFe, NiTi and mixtures thereof, and the dielectric film is formed of SiO 2 , Al 2 O 3 or a compound thereof.
Optical film, laminated structure, transmission density, aperture stop, light absorbing film, dielectric film

Description

ND filter and aperture diaphragm apparatus

1A and 1B are schematic side and cross-sectional views of a variable ND filter structure according to the present invention.

2 is a graph showing the permeation concentration characteristics of the variable ND filter according to the present invention.

3 is a schematic block diagram showing a vapor deposition apparatus used for the preparation of the variable ND filter according to the present invention.

4 is a table showing film deposition conditions for a variable ND filter according to the present invention.

Fig. 5 is a schematic diagram showing an aperture stop device for a camera using a variable density ND filter according to the present invention.

6 is a graph showing optical characteristics of the light absorbing film included in the optical film stack.

7 is a graph showing optical characteristics of an optical film laminate.

8 is a graph showing optical characteristics of an optical film stack.

9 is a graph showing optical characteristics of the optical film lamination.

[Patent Document 1] Japanese Unexamined Patent Publication No. Hei 6-95208

[Patent Document 2] Japanese Patent Application Laid-Open No. 10-96971

[Patent Document 3] Japanese Patent Application Laid-Open No. 2-47722

[Patent Document 4] Japanese Patent Application Laid-Open No. 2003-043211

The present invention relates to a neutral density filter (hereinafter referred to as an "ND filter") and an aperture stop device. The ND filter is used for a light amount stop for the purpose of uniformly attenuating the amount of transmitted light in the entire visible light wavelength range. The present invention relates in particular to concentration-variable ND filters, in which the permeate concentration is continuously varied.

In conventional photographic systems, if the luminance of an object is too high, even if the aperture is adjusted to the minimum diameter (that is, even if the aperture diameter is adjusted to the minimum), a large amount of excess light enters the photosensitive surface through the aperture. . Thus, in particular, an ND filter is mounted on the imaging system to control the amount of light entering the photosensitive surface. In this case, to simply reduce the amount of incident light, the spectral characteristics of the ND filter are designed to be flat, thus providing uniform transmission over the entire visible light wavelength range, depending on the basic optical performance of the ND filter.

ND filters with uniform transmission concentrations have been used as light quantity apertures in cameras. Recently, an ND filter that changes stepwise in a region where the permeate concentration is divided has been used as an improved filter. Furthermore, the use of a variable density ND filter compared to a single density ND filter or a multi density ND filter provides high resolution over a wide luminance range, so that for video optical systems that require continuous shooting, the concentration of the transmission density changes continuously. Variable ND filters are required. The variable concentration ND filter is disclosed in the patent documents described in the above-mentioned 'prior art document information'.

According to Patent Document 1, a master pattern of the ND filter is prepared, which has a predetermined relationship with the transmission concentration distribution of the ND filter which provides a filtering function for transmitted light when the ND filter is mounted on the iris blade of the aperture stop device. Has a reflection density distribution. This master pattern is picked up by a camera using a film having a film base transmittance of 80% or more and having an antihalation layer. After that, the film is developed and used as an ND filter. According to patent document 2, by the manufacturing method of the ND filter provided for the diaphragm wing of an aperture stop device, the plastic film containing an organic pigment is irradiated with the light of high energy, and the ND filter which has a variable concentration distribution is prepared. The amount of light irradiated is partially changed to make it possible. According to Patent Document 3, the ND filter uses a metal material as the absorbing film, and the amount of transmitted light varies continuously radially from the center where the antireflection film is formed. In this ND filter, the absorbing film is divided into multiple thin films, and the divided absorbing layers are inserted at the boundary of the antireflective film.

According to Patent Document 1, the change in the concentration of the ND filter is provided by changing the amount of precipitation of silver particles. However, light scattering due to silver particles causes resolution deterioration, and this type of ND filter is difficult to use in modern imaging systems with enhanced resolution. In patent document 2, the change with time of an organic pigment, especially the change of the permeation | transmission characteristic in a high temperature, high humidity environment is a serious weak point. According to Patent Document 3, a change in density is provided by locally inserting metal films having different thicknesses between antireflective films. According to this method, however, uniform transmission characteristics in the entire visible light wavelength range cannot be obtained, and therefore it is difficult to apply this type of ND filter to the imaging system.

In view of the various problems of the prior art as described above, an object of the present invention is to provide a concentration-variable ND filter having no light scattering, durability against environmental changes, and neutral transmission characteristics over the entire wavelength range of visible light.

In order to achieve this object, the following means are provided. In particular, the present invention comprises a transparent substrate having a plane, and an optical film laminate having a laminated structure formed on the plane of the transparent substrate and comprising a light absorbing film and a dielectric film and having a variable transmission concentration, The thickness of at least one layer of the absorbent film and the thickness of at least one layer of the dielectric film are changed in the inplane direction of the substrate, and the change is controlled so that the transmission concentration of the optical film is changed in the in-plane direction. An ND filter is provided.

Preferably, the thickness of the light absorbing film and the thickness of the dielectric film included in the laminated structure vary continuously or stepwise in the in-plane direction of the substrate, and according to this change, the transmission concentration of the optical film continuously in the in-plane direction. Adjusted to change. Moreover, the material of the light absorbing film is selected from titanium (Ti), chromium (Cr), nickel (Ni), nickel chromium (NiCr), nickel iron (NiFe), nickel titanium (NiTi) and mixtures thereof, and the dielectric film is It is formed of silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ) or a compound thereof. The dielectric film and the light absorbing film may be laminated in a predetermined thickness and in a predetermined order to provide an antireflection function. Moreover, the optical film stack is obtained by vapor deposition of a light absorbing film using a metal material, and the light absorbing film includes an oxide of a metal material produced during the introduction of a mixed gas containing oxygen during vapor deposition of the light absorbing film. And a vacuum level of 1 × 10 −3 Pa to 1 × 10 −2 Pa is always maintained. In this case, after the light absorbing film and the dielectric film are laminated, the optical film stack is subjected to a thermal aging treatment under an oxygen atmosphere containing 10% or more of oxygen, and the change in optical properties is saturated or stabilized. Such an ND filter may be attached to the iris blade of the aperture stop device.

According to the present invention, the ND filter basically has a laminated structure of a light absorbing film and a dielectric film formed on a transparent substrate. This laminated structure does not cause light scattering, and has durability against environmental changes and neutral properties for the entire visible light wavelength range. Since the thicknesses of the light absorbing film and the dielectric film of the laminated structure are changed in the in-plane direction of the substrate, the transmission concentration may be changed in the in-plane direction of the substrate while maintaining durability and neutral characteristics. Therefore, it is possible to obtain a concentration-variable ND filter which does not cause light scattering and has durability against ambient changes and neutral characteristics over the entire wavelength range of visible light.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 1 is a schematic cross-sectional view (a) and side view (b) of a variable density ND filter structure according to the present invention. As shown in FIG. 1A, the ND filter includes a transparent substrate 1 having a flat surface and an optical film stack 2 formed on the substrate 1. The optical film has a laminated structure including light absorbing films 22, 24, 26 and dielectric films 21, 23, 25, 27. When the thickness of the light absorbing films and the transparent dielectric films is controlled, a locally adjusted transmission concentration is obtained. As a feature, the thickness of at least one of the light absorbing films 22, 24, 26 and the dielectric films 21, 23, 25, 27 of the laminated structure varies in an in-plane direction of the substrate 1, and According to a change, the transmittance density | concentration of the optical film laminated body 2 is adjusted so that it may change in in-plane direction. In the embodiment shown in FIG. 1, the thicknesses of all seven layers constituting the ND filter are varied in the same ratio. However, the present invention is not limited to this embodiment. The thicknesses need not be changed in the same proportions, or all the thicknesses of the films need not be changed. Moreover, the total number of layers of the laminated structure can be freely determined according to the optical specification.

In this embodiment, the thicknesses of the light absorbing films 22, 24, 26 and the dielectric films 21, 23, 25, 27 of the laminated structure are in-plane directions (from left to right of the drawing) of the substrate 1. It is changed continuously in this, and according to this change, it adjusts so that the transmission density | concentration of the optical film 2 may increase continuously as it goes from the left side to the right side of a figure. In order to change the thickness of the film continuously or stepwise in the in-plane direction of the substrate, a shielding effect using the mask 3 can be used during the film deposition process, such as a vapor deposition process. For example, when the first dielectric film 21 is deposited, the mask 3 is moved from left to right at a constant speed as indicated by the arrow while performing film deposition at a constant deposition rate. As a result, a thin dielectric film 21 is obtained on the left side and thick on the right side. This process is performed repeatedly for all films, resulting in the inclined or tapered structure shown in FIG. 1A. It should be noted that constant movement of the mask 3 can be performed by a motor.

FIG. 1B shows a schematic cross-sectional structure taken along the BB line of the ND filter shown in FIG. 1A. The cross-sectional structure for the thickest portion of the ND filter shown in FIG. 1A is provided, the transmission concentration D of which is 1.4. As shown, the transparent substrate 1 was made of 0.1 mm thick PET (polyethylene tere-phthalate). However, the present invention is not limited to this material, and polyester film or polycarbonate (PC) film may also be used instead of PET. Polyester films or polycarbonate films such as PET are preferred for the aperture stop; However, unless the application is particularly limited, transparent glass or plastic may be used if necessary as the transparent substrate 1 for the wavelength range used. The first dielectric film 21 provided on the transparent substrate 1 is formed of SiO 2 and its physical thickness is 44 nm. The light absorbing film 22 formed on the dielectric film 21 is made of metal Ti and oxide Ti X O y , and its physical thickness is 55 nm. The dielectric film 23 provided on the light absorbing film 22 is made of Al 2 O 3 , and its physical thickness is 26 nm. The light absorbing film 24 provided on the dielectric film 23 is also formed of metal Ti and oxide Ti x O y , and its physical thickness is 80 nm. The dielectric film 25, which is the fifth layer provided on the light absorbing film 24, is made of Al 2 O 3 , and its physical thickness is 26 nm. The light absorbing film 26 provided on the dielectric film 25 is also made of metal Ti and oxide Ti x O y , and its physical thickness is 28 nm. The final seventh layer, dielectric film 27, is made of SiO 2 and its physical thickness is 78 nm. However, the disclosed laminated structure is only an example and, of course, does not limit the scope of the present invention. In the case of an optical thin film, a transparent ceramic material is generally represented as a dielectric film for the wavelength to be used. When the dielectric films having such thickness (approximately several times the wavelength) in which the optical interference effect appears, the optical properties (the amount of reflected light, the amount of transmitted light, the polarization and the phase) of the incident light can be freely adjusted. In this embodiment, by using the layer structure shown in FIG. 1B, the antireflection function is imparted to the optical film 2. Light absorbing films have a function of literally absorbing light in the wavelength range used, and metal is generally used in the visible light wavelength range. According to the invention, metal oxides are introduced into the metal material in order to specifically improve the optical and physical properties. Instead of Ti, other metals Cr, Ni, NiCr, NiFe, NiTi and mixtures thereof can be selected as the metal material for the light absorbing film.

2 is a graph showing the permeation concentration characteristics of the variable ND filter shown in FIG. 1. The vertical axis represents the transmission concentration (D) and the horizontal axis represents the wavelength (nm). In this graph, the thickness of the optical film 2 was used as a parameter and a total of eight levels is shown. The thickest part of the optical film stack (part shown in FIG. 1B) was defined with a thickness ratio 1.0, with thickness ratios of 0.86, 0.71, 0.57, 0.43, 0.29, 0.14 and 0.00 below. As is apparent from the graph, the portion having a thickness ratio of 1.0 has a concentration of D = 1.4, and the transmission concentration D hereafter decreases substantially in proportion to the thickness. Moreover, at all thicknesses, the transmission concentration characteristic is nearly flat in the visible range. In the ND filter of the present invention, the amount of transmitted light is uniformly attenuated in the entire visible wavelength range.

FIG. 3 is a schematic block diagram showing an example of a vacuum evaporation apparatus used to prepare the variable concentration ND filter shown in FIG. In addition to the vacuum evaporation method, a dense film forming method such as an ion plating method, an ion assist method or a sputtering method may be used as the film deposition method for making the ND filter. As shown in FIG. 3, the evaporation apparatus mainly consists of a vacuum chamber 11, and a film thickness monitor 12 and a film thickness controller 13 are attached to the top of the chamber 11. The substrate holder 14 for safely supporting the substrate, the substrate 15 for measuring the thickness of the film, and the evaporation source 16 are arranged in the chamber 11. Although not shown, the film thickness control mask shown in FIG. 1 is located between the evaporation source 16 and the substrate holder 14. Film thickness monitor 12 includes a light source, a spectrometer and a light receiver. Light emitted from the spectrometer is incident on the thickness measuring substrate 15, light reflected from the thickness measuring substrate 15 is incident on the light receiver, and the output from the light receiver is transmitted to the film thickness controller 13. In this way, because film thickness is monitored in real time, light absorbing films and dielectric films having the desired thickness are deposited on the substrate. At this time, the above-described mask moves simultaneously with the real-time monitoring of the film thickness, so that the light absorbing films and the dielectric films whose thickness is monotonously changed in the in-plane direction of the substrate are deposited.

The vacuum gate 17, the vacuum gauge controller 18, the gas inlet unit 19 and the exhaust unit 20 are connected to the chamber 11. In this embodiment, an APC system is used to maintain a constant degree of vacuum in the chamber 11. Specifically, feedback is made through the vacuum gauge 17 and the vacuum gauge controller 18 to control the gas inlet unit 19 and adjust the amount of mixed gas flowing into the chamber 11. However, the present invention is not limited to this system, and a system for using a needle valve may be used to maintain a constant inflow gas amount.

4 is a table showing film deposition conditions when the optical film shown in FIG. 1 is prepared using the vacuum evaporation apparatus shown in FIG. As shown in FIG. 4, the substrate temperature is 100 ° C., and the degree of vacuum reached in the chamber 11 is set to 1 × 10 −3 Pa. Ti is used as a raw material to deposit the light absorbing films 22, 24 and 26, and the evaporation rate is set to 1 nm / sec. Moreover, in this embodiment, air in which nitrogen and oxygen are mixed at a ratio of 4: 1 is used as the introduced mixed gas for evaporation of Ti. However, of course, the present invention is not limited to this gas, and a mixed gas containing oxygen is generally used at a rate of 50% or less. Moreover, the vacuum degree when the mixed gas containing oxygen flows in is set to 4x10 <-3> Pa. However, the present invention is not limited thereto. In general, when the degree of vacuum is maintained between 1 × 10 −3 Pa and 1 × 10 −2 Pa, light absorbing films made of a mixture of metals and metal oxides with desirable optical and physical properties may be deposited. SiO 2 is used as the evaporation source for the deposition of the dielectric films 21 and 27 and the evaporation rate is set to 1 nm / sec. No particular reactive gas is introduced for the deposition of SiO 2 . Al 2 O 3 is used as the evaporation source for the dielectric films 23 and 25 and the evaporation rate is set to 1 nm / sec. Also in this case, no reactive gas is used. As described above, when a metal material such as Ti is used, and when the partial pressure of oxygen in the mixed gas introduced during film deposition is adjusted, the light absorbing films consistent with the required properties can be used as metal films, or with metal films. It can be obtained as a mixture of oxide films. In order to stabilize the unstable elements included in the light absorbing films, heat treatment may be performed after film deposition. For example, after the light absorbing film and the dielectric film are laminated, the films may be heated under an oxygen atmosphere containing 10% or more of oxygen to saturate the optical performance change by this thermal aging treatment.

Fig. 5 is a schematic diagram showing an example in which the concentration-variable ND filter of the present invention is mounted on the iris blade of the aperture stop device of the camera. The diaphragm wing 100 is shown in FIG. 5, where reference numeral 0 denotes a variable concentration ND filter according to the present invention. As shown in Fig. 5, the transmittance of the variable concentration ND filter 0 decreases continuously from the center of the aperture opening toward the outside. That is, the transmittance of the variable density ND filter 0 decreases continuously and linearly in proportion to the distance from the optical axis of the imaging optical system.

The aperture stop is provided to control the amount of light incident on a solid-state imaging element such as a silver halide film or a CCD, and is reduced when the depth of field is bright. Therefore, the iris decreases when photographing objects of good weather or high brightness, and tends to be adversely affected by hunting phenomena or light diffraction of the iris, so that deterioration of image performance occurs. As a countermeasure, an ND filter is attached to the aperture blades to increase the aperture of the aperture even when the luminance of the depth of field is relatively high. In recent years, as the sensitivity of the imaging device is increased, the concentration of the ND filter is increased and the light transmittance is further reduced, so that the aperture of the aperture is increased even when the brightness of the depth of field is the same. However, as a problem, when the concentration of the ND filter decreases, the difference between the amount of light passing through the filter and the amount of light not passing through the filter increases, and the resolution decreases. In order to solve this problem, the concentration-variable ND filter shown in Fig. 5 is used. That is, in the concentration of the ND filter, when using the structure in which the transmittance of the ND filter is continuously and linearly increased in the optical axis center direction, the resolution decrease is prevented.

In this embodiment, a laminated structure in which light absorbing films and dielectric films are alternately laminated is used as the optical film stack forming the ND filter. Particularly in the light absorbing films, by using a composition containing a metal material and an oxide of the metal, reliability and durability of the concentration-variable ND filter are ensured over a long period of time. This point is described below for reference, and the details are described in Patent Document 4. First, FIG. 6 is a graph showing the optical characteristics of the light absorbing film deposited under the conditions listed in FIG. The horizontal axis represents wavelength and the vertical axis represents refractive index and absorption coefficient. As can be clearly seen from the graph, the absorption coefficient of the light absorbing film made of the mixture of Ti and Ti x O y in the visible light wavelength range tends to increase with increasing wavelength.

FIG. 7 is a graph showing the optical properties of an optical film having five layers prepared under the film deposition conditions shown in FIG. 4. The horizontal axis represents the wavelength in the visible light wavelength region, the left vertical axis represents the amount of light (%) indicating the scale of reflectance and transmittance, and the right vertical axis represents the transmission concentration. FIG. 7 shows simulation results obtained at the design stage instead of the properties of the optical film actually prepared. Ideally, the transmittance will eventually be flat over the entire visible wavelength range. In the design stage, the transmittance is gradually increased as it goes from the short wavelength side to the long wavelength side in consideration of the influence of the heat treatment to be performed later. This is because, as a characteristic of the optical film, it is predicted that the transmittance after heat treatment tends to increase toward the shorter wavelength in the visible light wavelength range.

FIG. 8 shows the initial properties of the optical film actually deposited under the film deposition conditions shown in FIG. 4. In order to easily understand the characteristics, reflectance, transmittance and transmittance concentration are measured as shown in FIG. 7. As can be clearly seen from the graph, the optical properties are substantially the same as those obtained in the design, and the transmittance gradually increases from the short wavelength side to the long wavelength side.

The optical properties obtained after the heat treatment are shown in FIG. 9. In order to understand the characteristics, reflectance, transmittance and transmittance concentration are measured as shown in FIGS. 7 and 8. As shown in the graph, after the heat treatment is performed, it is possible to obtain an optical film in which the transmitted light is uniformly reduced over the visible light wavelength range without any wavelength dependence and the reflection on the surface is suppressed. As described above, the transmittance is set in advance so as to gradually increase as it goes from the short wavelength side to the long wavelength side in the initial stage, whereby the optical characteristic change after the heat treatment is completed is compensated. By optimizing the deposition order of the dielectric films and the light absorbing films and the thicknesses of these films forming the laminated structure, the design as described above can be freely obtained. When the heat treatment is carried out, the transmittance tends to increase from the long wavelength side to the short wavelength side. Thus, the initial deflection is canceled, and as a result very flat transmission characteristics can be obtained in the visible wavelength range.

By changing the thickness of at least one layer of the light absorbing film or the dielectric film included in the optical film of the ND filter in the in-plane direction to provide a concentration-variable ND filter in which the transmittance of the ND filter is changed in the in-plane direction, without reducing resolution. It is possible to provide a high resolution, long life ND filter and a device having the same, which are prevented from deterioration.

Claims (7)

  1. A transparent substrate having a plane; And
    And an optical film formed on a plane of the transparent substrate and having a laminated structure including layers of a light absorbing film and a dielectric film and having a variable transmission concentration.
    The thickness of at least one layer of the light absorbing film of the laminated structure and the thickness of at least one layer of the dielectric film are changed in the in-plane direction of the transparent substrate, and the transmission concentration of the optical film laminate is changed in the in-plane direction,
    ND filter, characterized in that the reflectance of less than 5% in the region of the wavelength of the incident light is 450 to 750 nm.
  2. The method of claim 1,
    The thickness of the light absorbing film and the dielectric film included in the laminated structure is continuously changed in the in-plane direction of the transparent substrate, and the ND filter is controlled so that the transmission concentration of the optical film stack is continuously changed in the in-plane direction.
  3. The method of claim 1,
    The light absorbing film is formed of a material selected from Ti, Cr, Ni, NiCr, NiFe, NiTi, and mixtures thereof, and the dielectric film is formed of SiO 2 , Al 2 O 3, or a compound thereof.
  4. The method of claim 1,
    The dielectric film and the light absorbing film are successively laminated in a predetermined thickness and in a predetermined order to prevent reflection of light incident on the plane of the transparent substrate.
  5. The method of claim 1,
    The light absorbing film is formed by vapor deposition of a metal material, the light absorbing film comprises an oxide of the metal material formed during the inflow of a mixed gas containing oxygen during vapor deposition of the light absorbing film, the degree of vacuum during vapor deposition is 1 ND filter, characterized in that it is maintained at × 10 -3 Pa to 1 × 10 -2 Pa.
  6. The method of claim 5,
    The optical film is subjected to a thermal aging treatment under a gas atmosphere containing 10% or more oxygen, the ND filter, characterized in that the change in the optical properties of the optical film is saturated.
  7. An aperture stop device having an aperture blade mounted with an ND filter according to claim 1.
KR1020050040254A 2004-05-14 2005-05-13 ND filter and aperture diaphragm apparatus KR101111705B1 (en)

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JPJP-P-2004-00145541 2004-05-14
JP2004145541A JP4481720B2 (en) 2004-05-14 2004-05-14 ND filter and light quantity reduction device

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JP2003322709A (en) * 2002-04-30 2003-11-14 Sony Corp Thin film type nd filter
JP2004061899A (en) 2002-07-30 2004-02-26 Canon Electronics Inc Method for manufacturing nd filter, and nd filter, and light quantity reducing device and camera having such nd filter

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CN1696813A (en) 2005-11-16
CN100470269C (en) 2009-03-18
KR20060047909A (en) 2006-05-18
US7230779B2 (en) 2007-06-12
US20050254155A1 (en) 2005-11-17
JP2005326687A (en) 2005-11-24
JP4481720B2 (en) 2010-06-16

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